For years, machines have been used to scan parcels as they move along a conveyor. Over-the-belt optical character recognition (OCR) readers have been developed that can capture an image of the surface of a parcel as it moves along a conveyor, and then create and process a representation of the image. The fundamental physical components of an OCR reader are a sensor, an analog-to-digital (A/D) converter, and a computer comprising a memory. The individual physical components of an OCR reader are all well known in the art, and many alternative embodiments of each of the individual physical components are commercially available, with differing cost and performance characteristics. Much effort goes into finding the most efficient combinations of components for particular applications, and in the development of computer software programs that process the images created by these familiar physical components.
Charge-coupled device (CCD) sensor arrays are often used in OCR readers. A CCD camera consists of an array of electronic "pixels," each of which stores an accumulated charge according to the amount of light that strikes the pixel. A CCD camera is used to quickly capture an image of the surface of a parcel as it moves along a conveyor. The image is then converted into digital format which is then stored as a bit map in a computer memory. The CCD array is then reset by dissipating the charge within the pixels, and the array is ready to capture the image of another parcel. In this manner, a single CCD camera is used to scan a great many parcels.
CCD cameras vary in resolution and sensitivity. Generally, color cameras are more expensive than monochrome cameras; higher resolution cameras are more expensive than lower resolution cameras. There is therefore a financial motivation to use low resolution, monochrome CCD cameras whenever such are suitable for a particular purpose.
Similarly, computers vary in computation speed and other parameters. Generally, faster computers are more expensive than slower computers; special purpose computers are more expensive than general purpose computers. There is therefore a financial motivation to use low speed, general purpose computers whenever such are suitable for a particular purpose.
Parcel delivery companies, such as United Parcel Service (UPS), could make extensive use of OCR reader systems. These parcel delivery companies ship millions of parcels every day. The OCR readers used by parcel delivery companies such as UPS generate an enormous amount of computer data. As a result, there is a need for computer systems that can quickly and accurately process the images created by CCD cameras. For example, computer systems have been developed that can read the destination address written on certain parcels, and cause the parcels to be correctly routed to their destinations. Reading text is a sophisticated task, and the systems capable of doing so are commensurately sophisticated, comprising expensive equipment such as high resolution CCD cameras and high speed computers.
Before the text affixed to a parcel can be read, it is necessary for the location and orientation of the text to be determined. A fiduciary mark may be used to by an OCR reader system to ascertain the location and orientation of an object or text affixed to an object. A fiduciary mark is an indicia of known optical signature which is placed on an object to be scanned with an OCR reader. An OCR reader system scans a parcel bearing a fiduciary mark and locates the fiduciary mark. In this manner, a fiduciary mark which is placed in a known relation to the destination address block of a parcel can be used by the OCR system to locate the position of the destination address block. Similarly, an orientation specific fiduciary mark whose orientation is placed in a known relation to the orientation of the text within a destination address block can be used by an OCR system to ascertain the orientation of the text.
To the extent that certain tasks required of an OCR reader system that are less sophisticated than reading text can be performed by other less expensive equipment than that used to read text, the more expensive equipment required to read text can be more efficiently dedicated to the more sophisticated task of reading text. Ascertaining the position and location of a fiduciary mark is an example of a function required of an OCR reader system that can be performed with less sophisticated equipment than that which is required to read text. There is therefore a financial motivation to ascertain the location and orientation of fiduciary marks using systems comprising low cost CCD cameras and general purpose computers.
There are a number of well known image processing techniques that are used to process images stored in a computer memory. For two dimensional images, a two-dimensional bit map matrix stored in computer memory represents the pixels of a CCD array. An orthogonal coordinate system corresponds to the matrix. Thus, the bit map uniquely identifies the position of each pixel of the CCD array. Three-dimensional or higher-dimensional bit maps similarly represent three-dimensional or higher-dimensional images in a computer memory. Polar or other coordinate systems similarly define positions within the matrix.
Standard image processing techniques will be familiar to those skilled in the art including: using projection histograms, convolution filtering, correlation, computation of the center of mass of image areas, and edge image analysis including the Hough Method.
A fiduciary mark may comprise any shape or combination of shapes. Certain configurations are inherently more efficient to search for than others. For example, a circular configuration is efficient to search for because of its rotation-invariant nature. Thus, a circle does not require consideration in a multiplicity of angular orientations.
A number of U.S. patents teach circular fiduciary marks. For example, Miette, U.S. Pat. No. 5,103,489, describes a label, method and device for locating addresses on articles to be sorted. The system uses a preprinted label including an address locating mark comprising a rotation invariant component and an irregular component (i.e., an orientation-specific mark inside a circle). The processing technique first locates the circular image and then ascertains the rotational aspect of the irregular component. The software program ascertains the rotational aspect of the irregular image by comparing the image of the irregular component with a limited number of predetermined reference signals defining various discrete orientations (i.e., correlation).
The system described in Miette suffers from a number of disadvantages. For example, the use of a rotation-specific component makes the fiduciary mark less efficient to search for than a mark comprising only circular images might be. Moreover, it relies on an opaque fiduciary mark that cannot occupy the same area as the text comprising the address without partly obscuring the text. Therefore, the fiduciary mark must be o located in a known relation to the address block on every parcel to be scanned outside the area to be marked with text. As a result, such systems generally require preprinted labels or parcels comprising the fiduciary mark and specifying a markable area for placing text. Thus, there remains after Miette a need for a more efficient, more versatile fiduciary mark system.
A number of U.S. patents teach the use of a combination of circular images of different sizes to define orientation. For example, Keane, et al., U.S. Pat. No. 4,760,247, describes an optical card reader utilizing area image processing. The system reads lottery tickets with markable areas and ascertains the location and orientation of the markable area of a ticket by first locating and identifying three circular images printed on the ticket. Similarly, Acker, U.S. Pat. No. 3,8012,775, describes a method and apparatus for identifying objects. The system described is a bar code reader including a scan controller, video processor, and data processor. An object displaying a bar code includes two circular images, one located on each end of the bar code. The circular image on one end comprises a different pattern of concentric circles than the image on the other end, so as to identify the orientation of the bar code.
The systems described in Keane, et al. and Acker suffer from some of the same disadvantages as the system described in Miette. Namely, they rely on opaque preprinted fiduciary marks. There still remains after Keane, et al. and Acker the need for a more versatile fiduciary marking system. In particular, the parcel delivery industry has a need for a fiduciary mark system that can be applied to a parcel after the address has been affixed to the parcel. In this manner, the system will not rely on preprinted labels or parcels.
Fluorescent markings provide a means for reading indicia with a CCD camera wherein the indicia may occupy the same area as opaque text. When exposed to ultraviolet light, the fluorescent markings are readable by a CCD camera, while the text is relatively invisible. Conversely, when exposed to white light, the opaque text is readable by a CCD camera, while the fluorescent markings are relatively invisible. In this manner, both types of markings, opaque text and fluorescent indicia, can occupy the same area on a substrate.
Several references describe the use of fluorescent markings to highlight text bearing areas of objects to be read by CCD cameras. Buchar et al., Canadian Patent Application No. 2,047,821, describes an electronic filing system recognizing highlighted text within a document to be scanned to establish classification and retrieval information. A human operator examines a document to be registered into the system, and manually highlights with a fluorescent marking pen a portion of text which will be used by the system to identify the document. A raster scanning unit including a CCD array identifies the highlighted area when the document is scanned and records the text within the highlighted area for use by the retrieval system.
Ng, et al., U.S. Pat. No. 5,138,465, describes a method and apparatus for highlighting nested information areas for selective editing. Two fluorescent markings of different reflectivity are used in combination to define a combination of areas of interest (e.g., the area inside both markings, the area inside the area defined by one marking and outside the area defined by the other marking, etc.). The systems may use documents with pre-printed markings, or the markings may be applied with fluorescent marking pens after the text to be scanned has been affixed.
The systems described by Buchar et al. and Ng, et al. suffer from an important limitation. Namely, documents using these systems must be oriented properly when fed into a document scanner for the text to be read properly. While these systems teach the use of fluorescent markings to identify the location of text, they do not teach the use of fluorescent markings to specify the orientation of the text. Therefore, these systems would not be useful for reading text on the surface of a parcel as it moves along on a conveyor.
Thus, there is a great need for a flexible, easy to use, highly accuracy, inexpensive fiduciary mark system that can be used in conjunction with over-the-belt or other OCR readers. In particular, there is a great need for a fiduciary mark system that can process a sufficiently large number of images quickly enough to be used as an integral part of the automatic parcel handling systems used in the parcel delivery industry. To be advantageous, such a system should comprise a number of important advantages including: (1) the use of low cost components such as a low resolution monochrome CCD camera and a general purpose computer; (2) the ability to ascertain the location and orientation of the address block without relying on a standardized or preprinted label or container; (3) the ability to read fiduciary marks affixed to the parcel either before or after the address has been written on or attached to the parcel, without obscuring the address; (4) the ability to identify poorly formed or damaged fiduciary marks; (5) the ability to reliably reject false marks; and, (6) the ability to accomplish the identification in a highly accurate yet computationally efficient manner.